Extend the scope of setup_pcmd callback for resource managers, leave the current callback as it is but allow a new setup_job callback to replace it.  setup_job differs from setup_pcmd in two ways
Extend the scope of setup_pcmd callback for resource managers, leave
the current callback as it is but allow a new setup_job callback
to replace it.  setup_job differs from setup_pcmd in two ways

1) It returns it's results via a hash rather than the rather ugly
   list;
2) It can return a list of hosts rather than a command and have
   padb work out how to launch the job

This is good for the mpirun resource manager as it seperates out the 
quering of mpirun from setting up pdsh and should also be of use to
other resource managers who don't allow native launching of shadow
jobs

ashleypittman/padb,ashleypittman/padb,ashleypittman/padb